Engine torque sensors have been developed to help regulate and optimize various aspects of motor-driven vehicular performance. For example, to improve automotive vehicle driveability in powertrain applications, it is desirable to coordinate engine and transmission control functions. Transmission control algorithms in powertrains use torque information from the engine controller under a wide variety of powertrain operating conditions to improve shift quality, fuel economy, and drivability. Engine torque sensing is used to improve other aspects of performance, such as cold-start driveability, combustion optimization, and cylinder-balancing.
For internal combustion engines, in-cylinder pressure sensors have traditionally been utilized to estimate engine torque as a function of the pressure gradient during compression and power strokes. Other more complex modules have also been developed to estimate engine torque utilizing various combinations of sensors. For example, the in-cylinder pressure sensor may be combined with manifold pressure, air-flow, ambient pressure, and air temperature sensors to generate a cooperative engine torque estimation system. The limited accuracy and reliability of these estimation modules, however, present fidelity concerns that impede high performance engine and transmission control strategies currently prevalent in automotive vehicles. As subsystems, including those related to emissions, fuel economy and driveability, become increasingly more complex, their proper performance require more accurate torque determination, making conventional engine torque estimation methods insufficient to achieve the stated goals of new powertrain control strategies.
To achieve the objectives of faster and more efficient powertrain calibration, control, engine-transmission matching and improved driveability, direct engine torque sensors of laboratory quality have been developed in recent years. These sensory systems typically include a crankshaft-mounted sensor that directly measures the torque-induced strains in the crankshaft. For example, conventional crankshaft-mounted strain gauges have been electronically coupled to a communication bus through a series of slip-rings, insulators, and brushes. Another example includes a magnetoelastic application, wherein the crankshaft is elongated, and at least a portion of the crankshaft is initially magnetized. In this configuration, a collar sensor measures changes in the magnetic flux of the magnetostrictive material.
Conventional direct engine torque sensors, however, present various packaging, cost, performance, and reliability concerns. First, these sensors are relatively complex and expensive to produce in comparison to other vehicle components, and therefore, have yet to become fully implemented in the mass production of automotive vehicles. Another obstacle to mass production is the lack of required space on or near the crankshaft for sensor integration in production vehicles. No earlier attempts at installing the sensor on the crankshaft have led to a method viable for mass production, as they require significant engine modifications. Finally, the limited bandwidth typically presented in these sensors provide insufficient capabilities for optimization tasks, such as shift point optimization or spark timing control on an individual-cylinder individual-event basis for the full range of engine operating conditions.